This invention relates generally to pressure vessels and in particular to pressure vessels for holding high temperature material under high pressure that require periodic inspection of welds and internal structural members.
Reference is made to inventor's prior patent No. 4,767,593, for a multiple shell pressure vessel with interspace metallic fillers of which the invention disclosed and claimed herein is an improvement.
For pressure vessels containing toxic material at high pressures and temperatures, such as, nuclear reactors or containment vessels for toxic chemical reactions, safety requirements, such as those required by the American Association of Mechanical Engineers and other organizations both public and private, dictate periodic inspection and re-examination of all pressure loaded joints. The joints, such as, shell-to-flange girth welds and all other welds, must be exposed for non-destructive testing, such as, by ultra-sound, X-ray or other methods for determining soundness of a structure.
For a single wall pressure vessel of the prior art, assembly and disassembly of the vessel was fairly straightforward. All welds were generally readily available for inspection.
For a multiple-shell pressure vessel, the welded assembly of pressure vessel shells rendered it difficult, if not impossible, to gain ready access to the welded joints of the inner shells of the vessel without breaking or cutting the vessel apart.
For a single wall pressure vessel of the prior art, a crack in the shell could easily propagate through the wall causing a catastrophic failure. For a multiple shell pressure vessel, such as, the present invention, a crack in one shell-layer cannot propagate to the other layers.
For the present invention, overpressure may cause "gapping" of the modules as the tendons stretch, with subsequent "leak-before-break" failure mode. In this failure mode the vessel fluid will leak out into the external (water) coolant thus relieving the overpressure.
In addition, the prior art pressure vessels could fail due to excessive creep, or creep buckling. For the present invention, the tendons may be tightened and filler introduced in the outermost filler space, while the pressure vessel is in service, so that the main vessel shell layers will not be able to creep.
Furthermore, the single or multilayer pressure vessels of the prior art cannot be cooled through the vessel wall. Therefore, internal thermal insulation, or cooling of the internal vessel wall surface is necessary. For prior art pressure vessels, this posed an awkward problem. The insulation would be exposed to the vessel fluid and maintenance and repair was cumbersome.
For the present invention, the thermal insulation is located inside the wall and its outer surface and the outer vessel shells can be kept cool, due to good thermal bonding from metallic fillers in the interspaces between the outer pressure vessel shells, so that they can carry a larger pressure.